Atherosclerosis is a progressive disease of the vascular system whereby atheroma is deposited on the inner walls of blood vessels. Atherosclerosis is a complex, progressive and degenerative condition resulting in the build-up of cholesterol and other obstructive materials, known as plaque, on the walls of the arteries. The accumulation of plaque narrows the interior or lumen of arteries, thereby reducing blood flow.
Plaque occurs in the arteries in several different forms and may be located in many different anatomies throughout the arterial system. Plaque varies in composition, with portions that are hard and brittle, referred to as calcified plaque, and other portions that are fatty or fibrous. Over time atheromatous deposits can become large enough to reduce or occlude blood flow through the vessels, leading to symptoms of low blood flow, such as pain in the legs (on walking or at rest), skin ulcer, angina (at rest or exertional), and other symptoms. To treat this disease and improve or resolve these symptoms it is desirable to restore or improve blood flow through the vessel.
Various means are used to restore or improve blood flow through atheromatous vessels. The atheroma deposits can be displaced by diametrically expanding the vessel by inflating balloons, expanding stents, and other methods. The deposits can be pulverized using lasers and other methods. Atherectomy catheters can be used to remove atheromatous deposits from the blood vessel and may present an ideal solution when the atheromatous debris removed from the vessel is captured and removed from the body.
Many types of atherectomy catheter devices have been proposed, including catheters with rotating burrs, lasers to photodissolve tissue, and cutter-balloon catheters. All have challenges, however, such as traversing through small and tortuous arteries to get to the plaque occluded target zone or zones. This can be especially difficult if the treatment site has been totally occluded by the plaque. Another challenge lies in the inability to safely and efficiently handle and remove the plaque which is removed from the vessel walls during the atherectomy procedure. Some devices are not designed to handle the liberated plaque fragments at all and instead let the fragments migrate through the circulation. This can cause many problems because the liberated plaque remnants can be thrombogenic and can end up causing downstream occlusions. Other catheter designs reduce this problem by capturing the removed plaque in a collection or storage chamber so that it can be removed from the vessel.
One recent atherectomy catheter, the SilverHawk® articulated rotating blade atherectomy catheter, (sold by ev3, Inc.) has been designed to address these problems. The SilverHawk® catheter (features of which are exemplified in U.S. Pat. Nos. 7,771,444; 7,713,279; and 7,708,749 which are incorporated herein by reference in their entirety) uses a unique rotating blade, a side cutting window through which the blade can be extended, and a hinged nose design which can be controlled to cause the catheter to assume a straight position or an angled position. During the cutting procedure the catheter is in the angled position so the side cutting window and cutting blade can be urged against the vessel wall. The SilverHawk® catheter is moved distally through the lesion during the cutting procedure. The SilverHawk® catheter includes a collection chamber located in a distal portion of the catheter nose distal of the cutting window. The cutting blade and cutting window are configured to direct material cut from the vessel wall through the cutting window and into the collection chamber.
Although the SilverHawk® catheter represents a significant advance over prior art devices challenges remain for atherectomy catheters. For example, if the treatment site is a CTO (chronic total occlusion) it might not be possible to cross the lesion with the catheter. CTO's are sometimes comprised of hard, calcified material which is difficult or impossible to cross with either a standard guidewire or atherectomy catheter. If the CTO can not be crossed with the atherectomy catheter to enable it to be placed in a proper treatment position it can not be used to remove material from the treatment site and other, alternative treatments must be used.
Additionally, catheters that remove material, such as the SilverHawk® catheter, may include a collection chamber positioned distally of the cutting window. This requires that the length of the catheter distal of the cutting window be long enough to accommodate the collection chamber. This creates some conflicting design choices. On the one hand, it is desirable for the collection chamber to have a capacity large enough to accommodate a reasonable amount of cut material before the chamber fills and the catheter must be removed. On the other hand, the increased length of the catheter distal to the cutting window necessary to accommodate a sufficiently large collection chamber is disadvantageous in certain applications. For example, if the treatment site or lesion is located in a vessel with a particularly tortuous anatomy or small size there might not be enough accessible vessel space distal to the lesion to accommodate the distal length of the catheter distal of the cutting window. This accessible space distal to the treatment site is sometimes referred to as the “landing zone”. In order for the catheter to be used effectively the anatomy of the vessel must be such as to enable the catheter to be advanced far enough to position the cutting window within the treatment site and the distal portion of the catheter, which houses the collection chamber, in the landing zone. Thus, atherectomy catheters may be difficult to use in vessels with short landing zones.
In addition, during the cutting stroke, the atherectomy catheter may be pushed distally by the operator from the proximal end of the catheter through the treatment site with the cutting blade extending through the cutting window. It is possible during this pushing motion for the catheter to encounter resistance due to vessel size or tortuous vessel anatomy. This resistance can make it more difficult for the operator to control the catheter during use. The pushing motion can also compress the shaft of the catheter when resistance is encountered increasing the possibility that the shaft may buckle. If the resistance encountered with the pushing motion is abruptly released the catheter can jump in the distal direction, possibly causing injury to the vessel such as perforation or dissection. When a catheter is pulled proximally through a vessel the catheter body is in tension rather than compression. With tension there tends to be less stored energy, so a sudden release of resistance encountered with the pulling motion results in a lower possibility of jumping.